1. Field of the invention
The present invention relates to an exchangeable process cartridge used for forming an image and an image forming apparatus using the process cartridge, and particularly, to a process cartridge containing a light-sensitive carrier, a charging unit and a developing unit and an image forming apparatus using the process cartridge.
2. Description of the Related Art
Image forming apparatuses, such as a copying machine, a printer and a facsimile, employ a latent image forming type recording apparatus like an electrophotographing apparatus, due to a recent demand for image recording on normal sheets of paper. According to this image forming principle, after a photosensitive drum is precharged, the photosensitive drum is exposed to a light image to have an electrostatic latent image formed thereon. This electrostatic latent image is developed by a developing unit so that a toner image is formed on the photosensitive drum. This toner image is then transferred onto a sheet of paper to obtain the toner image on the sheet.
These image forming process units, such as the photosensitive drum etc, have a limited service life due to the functional deterioration of the photosensitive drum, filling up of toner collected in a cleaner, contamination of a charging unit and abrasion of a developing roller of the developing unit during the use of the apparatus. Therefore, it is necessary to exchange a process unit with a new one. In particular, in a case of compact image forming apparatus, the interval of the exchange is shorter as it is constituted in a smaller size.
On the other hand, it is troulbesome for users that they exchange individually each process unit installed separately. And it is further requiring to adjust a position of the process units each other. For this reason, it is effective to provide a means allowing the users to exchange an expired cartridge with a new cartridge by installing these unit in a single cartridge. According to this way, it is convenient for the users, as they can exchange a plurality of units by single handling and are not requested to make adjustment such as positioning of units. For the process cartridge described above, the ones which can be exchanged easily, being exchangeable of the expired unit alone, are preferable.
FIGS. 1A and 1B are explanatory diagrams of prior art. As the process cartridge described above, two types of process cartridge are known. One of which type installs every process unit in a single cartridge as shown in FIG. 1A, and the other type installs a part of process units in a single cartridge as shown in FIG. 1B.
The type shown in FIG. 1A is a process cartridge 150 provided with a photosensitive drum 151, a charging unit 152 for charging the photosensitive drum 151, a cleaner 153 for removing and collecting the residue toner on the photosensitive drum 151 and a developing unit 160 for developing an electrostatic latent image on the photosensitive drum 151. According to this process cartridge 150, time and labor for the exchanging can be reduced, as all of the process units except optical unit for exposing to a light image and transfer unit can be exchanged together by pulling out the cartridge. However, in a case of this process cartridge 150, if the service life of the photosensitive drum 151 alone expired, the developing unit 160 should be exchanged at the same time before its service life actually expire. If the service life of the developing unit 160 expired, the photosensitive drum 151 should be exchanged likewise at the same time before its service life actually expire. Therefore, in this constitution, it will be a waste of resources.
In the scope of this constitution, a contact type developing unit, which develops an image by contacting a developing roller with the photosensitive drum, is known as a developing unit. When the contact type developing unit is employed, it is required that the contact pressure of the developing roller with the photosensitive drum is a constant, for obtaining a stable developing operation. However, according to the constitution of prior art, there is a fear that a stable developing operation becomes difficult, as the pressure of contact fluctuates due to external factors.
On the other hand, FIG. 1B illustrates a process cartridge provided with a photosensitive drum 151, a charging unit 152 for charging the photosensitive drum 151 and a cleaner 153 for removing and collecting the residue toner on the photosensitive drum 151. It means that the developing unit 160 is separately provided from the process cartridge 154. This constitution is based on the idea that the exchange of both developing unit 160 and photosensitive drum 151 at the same time is uneconomical since the service life of the developing unit 160 can be extended by supplying toner or the like, thereby making the service life thereof longer than that of the photosensitive drum 151. In this constitution, it is possible to exchange any of the cartridge 154 alone, the developing unit 160 and both of the cartridge 154 and the developing unit 160.
However, it is necessary to pull out the cartridge 154 from the apparatus prior to the exchange of the developing unit 160, since the cartrige 154 is provided above the developing unit 160. And if both are exchanged, it is necessary to pull out the both respectively from the apparatus, then set them respectively to the apparatus. Therefore, time and labor are required for pulling out them from the apparatus and setting them to the apparatus. Furthermore, since the cartridge 154 and the developing unit 160 are separately provided in the apparatus, a positioning mechanism for the cartridge 154 and the developing unit 160 is required in the apparatus, thus the mechanism of whole apparatus is brought to a complication.